diff --git a/Makefile b/Makefile
index b0cd8d5..a9e1d6f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CC = gcc
-CFLAGS = -g -Wall -Werror -Wextra -Wformat=2 -Wjump-misses-init -Wlogical-op -Wpedantic -Wshadow
+CFLAGS = -std=c99 -g -Wall -Werror -Wextra -Wformat=2 -Wjump-misses-init -Wlogical-op -Wpedantic -Wshadow
 #CFLAGS = -ansi -g -Wall -Werror -Wextra -Wformat=2 -Wjump-misses-init -Wlogical-op -Wpedantic -Wshadow
 #CFLAGS = -Wall -Werror -Wextra -Wpedantic 
 EXECUTABLE = ls
diff --git a/ls.c b/ls.c
index 8b0c585..6ca16fb 100644
--- a/ls.c
+++ b/ls.c
@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 200809L
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -8,6 +9,7 @@
 #include <libgen.h>
 #include <limits.h>
 #include <stdarg.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -15,6 +17,10 @@
 #include <time.h>
 #include <unistd.h>
 
+#ifndef PATH_MAX
+#define PATH_MAX 4096
+#endif
+
 void ls_ent(const char *path);
 void do_regfile(const char *path, const struct stat *sb);
 void do_dir(const char *path, const struct stat *sb);
@@ -50,28 +56,20 @@ ls_ent(const char *path)
 	if (lstat(path, &sb) == -1) {
 		err(1, "Failed to stat %s", path);
 	}
-	switch (sb.st_mode & S_IFMT) {
-	case S_IFREG:
+	if (S_ISREG(sb.st_mode)) {
 		do_regfile(path, &sb);
-		break;
-	case S_IFDIR:
+	} else if (S_ISDIR(sb.st_mode)) {
 		do_dir(path, &sb);
-		break;
-	case S_IFLNK:
+	} else if (S_ISLNK(sb.st_mode)) {
 		do_symlink(path, &sb);
-		break;
-	case S_IFCHR:
+	} else if (S_ISCHR(sb.st_mode)) {
 		do_char(path, &sb);
-		break;
-	case S_IFIFO:
+	} else if (S_ISFIFO(sb.st_mode)) {
 		do_fifo(path, &sb);
-		break;
-	case S_IFSOCK:
+	} else if (S_ISSOCK(sb.st_mode)) {
 		do_socket(path, &sb);
-		break;
-	default:
+	} else {
 		do_unknown(path, &sb);
-		break;
 	}
 }
 
diff --git a/readme.rst b/readme.rst
index 00914a8..4c48632 100644
--- a/readme.rst
+++ b/readme.rst
@@ -4,3 +4,10 @@ ls
 
 
 above was spellchecked by claude3
+
+fts()
+isatty()
+getopt()
+strmode()
+
+c99